Acoustic object detection system and method

Abstract

A standing wave field is generated within a protected space, the standing wave field comprising a plurality of signals traveling along a plurality of propagation paths within the protected space, the propagation paths including reflections of the signals off of objects within the protected space. A change in a predetermined characteristic of the standing wave field is detected upon the changing of a physical characteristic of an object within said protected space, and an alarm signal is generated when said change in the standing wave field is greater than a predetermined threshold value.

We claim: 
     
       1. A system for detecting an object within a protected space, comprising: means for generating a standing wave field within a protected space, the standing wave field comprising a plurality of signals traveling along a plurality of propagation paths within the protected space, the propagation paths including reflections of the signals off of objects within the protected space;   means for detecting a change in a predetermined characteristic of the standing wave field upon the changing of a physical characteristic of an object within said protected space, the physical characteristic being the presence or absence of the object in the protected space; and   means for generating an alarm signal when said change in the standing wave field is greater than a predetermined threshold value to detect the presence or absence of the object in the protected space.   
     
     
       2. The system of claim 1, wherein said physical characteristic of the object further comprises the movement of the object within the protected space. 
     
     
       3. The system of claim 2, wherein said change detecting means comprises means for detecting a change in amplitude of the standing wave field. 
     
     
       4. The system of claim 3, wherein said change detecting means further comprises means for detecting a change in phase of the standing wave field. 
     
     
       5. The system of claim 4, wherein said detecting means further comprises means for comparing one of the phase or the amplitude of the standing field wave to a stored value of one of the phase or the amplitude to determine a change in the standing wave field. 
     
     
       6. The system of claim 5, wherein said comparison means comprises means for storing a value of the predetermined characteristic at a prior time, means for generating an update signal, and means for updating said stored value based on said update signal. 
     
     
       7. The system of claim 6, wherein said means for generating the update signal comprises means for automatically determining the time period of the update signal for a particular protected space. 
     
     
       8. The system of claim 6, wherein the protected space comprises one of an enclosed air space or a partially enclosed air space. 
     
     
       9. The system of claim 6, wherein said protected space comprises one of a partially enclosed underwater space or an enclosed underwater space. 
     
     
       10. The system of claim 2, wherein said change detecting means comprises means for detecting a change in phase of the standing wave field. 
     
     
       11. A system for detecting an object within a protected space, comprising: means for sampling an acoustic standing wave field generated within a protected space, the standing wave field comprising a plurality of signals traveling along a plurality of propagation paths within the protected space, the propagation paths including reflections of the signals off of objects within the protected space;   means for detecting a change in a predetermined characteristic of the standing wave field when a physical characteristic of an object changes within said protected space, the physical characteristic being the presence or absence of the object in the protected space; and   means for generating an alarm signal when said change in the standing wave field is greater than a predetermined threshold value to detect the presence or absence of the object in the protected space.   
     
     
       12. The system of claim 11, wherein said physical characteristic of the object further comprises the movement of the object within the protected space. 
     
     
       13. The system of claim 12, wherein said detecting means comprises means for detecting a change in amplitude of the standing wave field. 
     
     
       14. The system of claim 13, wherein said change detecting means further comprises means for detecting a change in phase of the standing wave field. 
     
     
       15. The system of claim 14, wherein said detecting means further comprises means for comparing one of the amplitude or the phase of the standing field wave to a stored value of the one of the amplitude or phase to determine a change in the standing wave field. 
     
     
       16. The system of claim 15, wherein said comparison means comprises means for storing a value of the predetermined characteristic at a prior time, means for generating an update signal, and means for updating said stored value based on said update signal. 
     
     
       17. The system of claim 16, wherein the protected space comprises one of an enclosed air space or partially enclosed air space. 
     
     
       18. The system of claim 16, wherein said protected space comprises one of a partially enclosed underwater space or an enclosed underwater space. 
     
     
       19. The system of claim 12, wherein said detecting means comprises means for detecting a change in phase of the standing wave field. 
     
     
       20. A method for detecting an object within a protected space, comprising: sampling a standing wave field generated within a protected space, the standing wave field comprising a plurality of signals traveling along a plurality of propagation paths within the protected space, the propagation paths including reflections of the signals from objects within the protected space;   detecting a change in a predetermined characteristic of the standing wave field when an physical characteristic of the object changes within said protected space, the physical characteristic being the presence or absence of the object in the protected space; and   generating an alarm signal when said change in the standing wave field is greater than a predetermined threshold value to detect the presence or absence of the object in the protected space.   
     
     
       21. The method of claim 20, wherein said physical characteristic of said object further comprises movement of the object within the protected space. 
     
     
       22. The method of claim 21, wherein said detecting further comprises detecting a change in amplitude of the standing wave field. 
     
     
       23. The method of claim 22, wherein said change detecting further comprises detecting a change in phase of the standing wave field. 
     
     
       24. The method of claim 23, wherein said detecting further comprises comparing one of the amplitude or the phase of the standing field wave to a stored value of one of the amplitude or the phase to determine a change in the standing wave field. 
     
     
       25. The method of claim 24, wherein said comparison comprises storing a value of the predetermined characteristic at a prior time, and updating said stored value periodically to track variations within the protected space. 
     
     
       26. The method of claim 25, wherein the protected space comprises one of an enclosed air space or a partially enclose air space. 
     
     
       27. The method of claim 25, wherein said protected space comprises one of a partially enclosed underwater space or an enclosed underwater space. 
     
     
       28. The method of claim 21, wherein detecting further comprises detecting a change in phase of the standing wave field. 
     
     
       29. A system for detecting an object within a protected space, comprising: a transmitter that transmits an acoustic signal into a protected space;   a detector that detects an acoustic standing wave field with the protected space, the standing wave field comprising a plurality of signals reflected from objects within said protected space;   a detector which measures the value of a predetermined characteristic of said standing wave field when a physical characteristic of an object changes within said protected space, the physical characteristic being the presence or absence of the object in the protected space;   a comparator that generates a comparison value from said predetermined characteristic value and a stored predetermined characteristic value; and   an alarm signal generator that generates an alarm signal when said comparison value is greater than a predetermined threshold value to detect the presence or absence of the object in the protected space.